I am also running on a low-spec machine.
And the game took a fair amount of time (almost a minute?) the first time I loaded it. It had a bit of slow down for a few seconds, but after that it started to run normal.
This game was quite difficult to judge for me, as I think it has pretty much potential. But in it's current state it wasn't so much fun to play.
Some parts feel pretty polished and nice like:
The graphics and behaviour of the different shot types, the enemy laser attacks, the sound effect and music or that nice title art.
On the other hand there were some things, that needed more polishment:
Level design:
it seemed like the enemies were just randomly placed, which isn't neccerally a bad thing. The problem was, that it was lacking the feel of progression. It just seemed to spawn randomly all kinds of enemies at once. If instead it would start with just spawning this one enemy for a while, then switch to another, then you get a lot of big ships only... and so on. It would feel more like the player is progressing and the level would feel less repetitive. There seemed to be a bit of this variation in the game, but I think it could be more emphasized.
Enemy movement:
Actually simple movements are nice and fitting for shmups. But i felt there was not much variation. Maybe because all enemy types kept respawning all the time. But still it felt somehow lacking polishment. For example the one enemy type which scrolls at the same speed as the background. This looks strange as they feel somehow glued to the background. And then the enemies on the rails, I actually liked the laser shooting ones. But since the rails were there for the entire level on the same spot it felt somehow repititve. If the rails would scroll in at a certain position and also end. And that could be expanded to varying x-position not just the sides. That would probably make the level design way more exciting. And then the suddenly appearing boss, it killed me while it appeared. As I moved to the top of the screen, something I often do in shmups to get the chance to attack the boss while scrolling into the screen. But in this case the boss instantly spawned at my position and killed me.
And then there is this huge player sprite with it's mini hitbox which feels pretty confusing.
So what I want to say is, that the game isn't bad or anything. Just due to the level design it was not that much fun to play as it could have been. With just a bit more tweaking in this regard it actually had the potential to be a pretty fun game. So I hope you don't get my critics wrong.
Now about the time freeze mechanic:
You seemed to really put your attention on that feature and it works pretty well. The different shot types and the time freeze mechanic feel pretty polished the way are installed.
It is only natural for complex control schemes to be a bit difficult to get into. Or to design them in a way, that the player gets more easy to them.
So, I also needed a few tries to get into the concept. But after getting used to the controls, they started to feel more comfortable. The most confusing thing for me was, getting used to the different attacks during the time freeze. Esspecially as I always forgot which mode I was in when I used the bomb. After a while I realized that in homing mode I have that reticle in front of my ship, which helped a lot. The green markers in the other mode weren't that helpful though. Maybe instead of green markers you could have placed shadows of the ship, as that is what those markers actually are turned into after the freeze stops and would help the player understand what he is doing right now.
Though after a few tries I finally started to get the rough hang of it, but still was a bit unconfident with it's use.
That might be due to the meter filling pretty slow, this way the player gets not that often the chance to play around with the mechanic. And if he messed up he have to wait all the time until the meter refills. Also psychological I don't want to waste the long filled meter for experimentation but rather for survival.
Some other thoughts to emphasize the modes, maybe change the colour of the ship(?)
Like green for standard and blue for homing.
Or give the player 2 shot buttons and skip the change button:
z = standard
x = homing
(when the player presses both there's no reaction)
So when the player uses the time feature he can then decide which of the features he uses by pressing one of these buttons during time freeze. I.e.
I press shift for activating the time freeze, then I have the freedom of choice how I'd like to use it. If i see a lot of small enemies around me I'll get near them press x, and the reticle appears (when the reticle has appeared the game won't correspend to the z button during the time freeze).
These are just some ideas though. Overall the time freeze mechanic was pretty good.
In the end it is nice to see you implementing a complex control scheme into your prototype that actually works good. Which alone is quite a task to do and is also fun to play around with as a player. The game itself is not bad, but I felt it could be improved here and there to make it more fun. Probably we'll see some of those improvements in your next prototype.