Looking at the comments, I personally didn't run into the two upgrade bug (I have a pretty beefy PC, I think that's why) and got to the moon. Super cool little experience! I like how the swing keeps swinging after you jump off so you can hop back on without losing much speed.
I'm gonna take a wild guess and say that the the swing ropes are made of dozens and dozens of hinge joints or some non-Unity equivalent type physics object which is causing tons of lag. If you plan on updating this, I would recommend making them each longer and less of them. Might look a little line-y but probably the best compromise. Fun game!