So glad for this one! Over the last few years, the more and more features that have been added to Reason seem to have bogged it down a bit. For some it is worse than others. Today they just released a performance update for VST (and RE) and Reason in general. I had a few recent projects that were giving me the old "Computer is too slow to playback song" error. That seems to be a non-issue as I am opening these previous projects and playing thru/looping them without a pop click or error message. Reason 10.3 appears to use MUCH LESS DSP. Let me know if it changed anything for you and your system. Did for me! 👍
The official propellerheads announcement on Reason 10.3: