If you haven’t already done so, see if just upgrading to 3.0.4 will fix your problem.
In the case of projects that are already excessively slow, AudacityRescue (see 3.0.3 experiencing extreme slowdown and is Not Responding - #18 by jademan ) can be run to remove excess baggage and 3.0.4 can be used to keep them from coming back.
Unfortunately, you currently need a Windows machine to run AudacityRescue. If you do not have one available, zip up your project and upload it to a file sharing service. Post a link, or PM it to me. I’ll look at it.