Will using fan on central AC run up the bill?

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Using anything electrical will cost money.

I would get a nest and turn it on cash saving feature which regulates your furnace to be bill friendly.

I don't think running the fan for 15 minutes would cause the electric bill to go up

Hey Matthew, if you have a normal forced air furnace / AC in the house the main blower will use around 800-900 watts when running at full speed. (Some higher efficiency units have variable speed fans, but turning on fan only generally runs it on high). Most areas of the country have electric rates from 9 cents to 24 cents per kWh. Let’s assume yours is 15 cents. A 900 watt blower will use .9 kWh for each hour it runs. If you run it for 4 hours per day, 4 X .9 = 3.6 kWh, or about 54 cents per day, which comes to $16 a month, give or take a bit. A quick rule of thumb is about $4 a month for each hour per day the blower is running.

The AC compressor running with the blower on high uses closer to 3500 watts, or about 4 times the blower only. Hard to gauge how many hours AC runs in a 24 hour period though since it cycles differing amounts of time all day and night. We run our blower only here sometimes for maybe 45 minutes in the evening before bed just to circulate some of the cooler basement air into the bedrooms, never really notice it on my electric bill. Hope this clears it up a bit, take care, Rudydoo.

set the fan to "auto" on the thermostat and forget it.  it will run only as the system needs to cool off your space

Your question makes no sense. How are you going the run the AC when you are running the fan or are you just going to run the fan. How will you turn on the fan every 15 minutes? Under you scheme I can't tell when the AC will be running. It will have to run when required to maintain the 74 degrees that may be severe 10 minutes or every 25 minutes. It just depends on the house and the outside temp

If you're using electricity and not producing that 100% by yourself (such as solar), then your bill is going to be higher than if you don't use electricity.  Having a fan on uses electricity.  

HOW MUCH that costs depends:   Your unit's efficiency; Your electricity rates; and Your definition of 'a lot'.  

if doing that make you comfortable at 74 then it be much cheaper that dropping the temperature. An depending on the age of the unit also will determine power consumption.  newer equip especially ones wjt variable speed an ECM motor afe much mkre efficient. 

fan without the AC part functioning will cost money (power consumption) but less than if you run the AC part with the fan.  Impossible to be generic as to cost because it depends on the unit's power consumption.

I have no idea what you mean, but I have the bedroom A/C set to 73F and I have a floor fan on the on the end of the room blowing the cold air back at me.   Works just fine.