I have a Lennox G60DFV downflow 2 stage furnace with a White-Rogers control board.
Stage 1 (Low heat stage) of furnace is 68% of stage 2 high heat. Going to stage 2 right from the start will let you get to the desired temp some 5 (corrected) minutes earlier (depending on ambient outside temp.).
You said that the furnace runs in stage 1 for 15 minutes before switching to high heat. On my furnace control board, DIP switch #3 allows you to select high heat after a 10 or 15 minute minute run in low heat (10 minute delay with switch ON). Changing the delay for high heat to 10 minutes will help you.
To conclude: setting high heat delay from 15 minutes to 10 minutes and starting temperature recovery some 5 to 10 minutes earlier will give you the same results as a 2 stage thermostat (2 stage thermostat also needs at least one additional wire).
P.S. On my furnace, you have to change the setting of jumper E20 before going to a 2-stage thermostat.
I mentioned a saving of 5 minutes in high heat only.
Here is a more accurate calculation:
Assume a 80,000 BTU/hr high output and a 70% low heat output of 0.7 x 80,000 = 56,000 BTU/hr.
Assume furnace takes 1 hour to reach desired temp with 15 minutes on low heat.
15 min. on low heat = 56,000 x 15/60 = 14,000 BTU
45 minutes on high heat = 80,000 x 45/60 = 60,000 BTU
Total output in 1 hour = 14,000 + 60,000 = 74,000 BTU.
Time to produce 74,000 BTU in high heat only =
= (74,000/80,000)x60 = 55.5 minutes.
Conclusion: going to high heat from the start saves 4.5 minutes to raise temperature by 2*C
[Edited by deme on 03-11-2006 at 11:55 AM]