I had a look at the project. I can't reproduce any significant performance difference between r295 and r297. In both cases the CPU is around 50-60% and it runs about equally smoothly. The GPU utilisation increased slightly in r297, probably due to a rendering change to improve how transparency is handled, but it didn't appear to affect the smoothness much.
The events are pretty inefficient. In particular a great deal of CPU time goes on two actions that adjust the Z order of a couple of hundred "Billboard_Grass" objects with the "Move in front" action, which is done apparently redundantly every frame. The engine doesn't handle this efficiently at the moment, but it's a poor solution for Z ordering anyway - use layers, Z elevation, or if necessary, only run those actions when something actually changes, rather than all the time. If I delete those two events I don't actually see any obvious visual change and the CPU usage drops a lot.
It also creates around 1000 objects which seems a lot for a relatively simple style of game like this - perhaps you're creating hundreds of unnecessary objects and running intensive events on them all?
It's also difficult to test this reliably, as it seems to be based on randomised and procedurally generated content, which makes doing a fair comparison between two releases difficult. What if one time it generates a lot more content? It could be slower because of the content, not because you switched release. You have to be scientific about performance and make sure you're running exactly the same thing in each case and only vary one thing. It seems possible that there is no significant performance change in Construct and the content differences gave you a misleading impression of a performance change. From an engine point of view it is also much, much easier to investigate performance differences with a minimal project (as per our bug report guidelines).
I'm afraid I don't have time to dig any deeper, but in short I can't see any evidence of a major performance difference between r295 and 297 here, and the most serious problems look like inefficient events or game design, which are up to you to change! As ever it's important to keep an eye on the performance numbers and watch out for any changes that cause a big change to the numbers, which is an indication you made a change that hit performance, so you would probably want to find a better way to do that. And if you want to track down something that might be slow, split events up in to smaller groups to get better numbers from the performance profiler, and try deleting chunks of events to see if performance improves when to remove specific events.