Heater takes a long time to heat up

My 03 Jeep G.Cherokee takes forever for the heater to warm up. All systems work fine, but it seems as if, on startup, I just select the floor vents instead of the upper vents for or so, it will heat up faster.15 minutes. Is this a themostat issue?

Selecting different vents makes no difference, except perception. If you leave the heat off, how long does it take to reach operating temperature (on the temp gauge)? How cold is your climate right now? Are you idling or driving while this happens?

Sounds like a thermostat issue. It is pretty easy to change and not very expensive.