I agree that 64 RPM is low for such a low gear. No offense, but we warmup at 80-90 RPM on a 48/16 or 47/15 (3 gear inches higher) for 15-20 minutes on the track. That's a normal warmup even for beginners.

I say once or twice a week (depending on how often you do this ride), instead of doing 5 or 6 laps, try to do one lap pacing your self but going as fast as possible (safely, of course). Then take a break off the bike for 15 minutes then do it again. Get a speedometer and start noting your average speeds.

Eventually, you'll be able to hold those faster paces for 1 lap...then 1.5 laps...then 2 laps...Then you'll be asking for the nearest velodrome