How important is upgrading the furnace when installing a heat pump?

My partner are new homeowners. Our AC stopped working, and since it’s 15 years old, we figured all money should go toward replacement, rather than seeing if a repair tech can buy us another season.

All of the hvac quotes we’ve gotten include replacing the furnace as well. Our furnace (Carrier Infinity) is 15 yo too, but seems to be doing fine. I think one of the salespeople said that it could be compatible with the variable fan speeds of a heat pump. Besides, wouldn’t the heat pump reduce the overall use/wear on the furnace and prolong its lifespan? We’re in Minnesota, so a backup heat source is required, and keeping gas is (unfortunately) cheaper than running a fully electric system at this point.

Basically, the heat wave is here, it’s all very expensive, and we can’t tell if there are strong enough reasons to replace the furnace now, especially when electric could be more affordable by the time the furnace actually needs replacing.

House is about 1800 sq feet, walls are fully insulated, the attic needs some more insulation, windows are efficient enough upstairs but need some love in the basement.