I was going to ask if you were rendering your song using Arguru Sinc interpolation, because in my past experience that method was excruciatingly slow and never made any noticeable difference to audio quality.
But I just did some testing with my fairly mediocre Core i5 laptop and the latest incarnation of “Precise (HQ but slow)” interpolation is actually pretty fast. By far the biggest impact on rendering performance for me is choosing “High (as fast as possible)” rather than “Low (render in background)” for the Priority setting.
If your rendering is noticeably slow (it should be faster than playback, because if it were slower than playback that would suggest that Renoise can’t even play the song in realtime without skipping), I echo the suggestion to post your PC specs here because it might be you have some other bottleneck.
(I’d be surprised if the bottleneck was hard drive performance because we’re only talking about a basic PCM stereo audio track here, not multiple tracks or video. Even a 24-bit render at 48000 Hz only requires around 290 KB/sec which was easily achievable by IDE hard drives in the early 90s).