I purchased a Patton model PUH682 in October

I would think the contacts are burning out on the line voltage thermostats. The contact areas have been reduced over the years so they last just past the warranty period. If it were mine, I'd locate a line voltage baseboard heater thermostat and adapt the control to operate the heater elements. Much higher amp rating and built more substantially.

My Mighty Heater 1500 will run for 15sec then shuts off then repeats it over an over

Must be an older model heater. All the recent ones have a 3 prong plug. Especially, since the recall a couple of years ago on the PUH680-U Heater.

Yes, there is/was a recall on some Patton Heaters, but I don't recall if your model # is one of them. For more info search Google for Patton Heater Recall Notice and you'll find the correct site.

My Patton PUH682 utility heater from 2011 is otherwise in excellent condition but Auto Safety Shut-Off seems to be a design problem. My overheat sensor quickly shut off the unit when surrounding air was cool. It is inside the bottom of the fan box wired between the on/off potentiometer and heating coils.
I identified it by turning on the heater and watched the metal contacts separate as it tripped. On my unit, the defective overheat sensor is hardwired. Since it was otherwise useless as a heater, I decided to jerry-rig it and hope for the best. I pried back the sheet metal edge of the fan box and wrapped the sensor with electrical tape. Then I took a very small squeezable metal paper clip and lined it with electrical tape. I clamped it over the overheat sensor and it fits perfectly to prevent the metal plates from separating. Now the heater works the way it should. The cable, coils and plug don't overheat on Hot setting and it runs continuously.

I saw your post and I encourage you to report your problem to The U.S. Consumer Product Safety Commission. I called them to report the problem. The number to the company (Patton) is 763 444 8567. The number to The U.S. Consumer Product Safety Commission is 1-800-638-2772. The U.S. Consumer Product Safety Commission will take your report and if you know others that have this product and they have experienced the same thing encourage them to call and report it. The heater I had melted unto a ultility extention cord and was smoldering. It could have cause serious injury or damages to me and my family.

If this product could have injured you as well. The are a public hazard and need to be recalled.

If it was banged in any way some thing got stuck to it need to inspecked it

Under the main black knob is a bi-metal switch which shuts down the heat at various temps depending on your setting. Their is no timer.

If you need further help, reach me via phone at https://www.6ya.com/expert/dan_73bbd84fe1d95b61

I'm not all up on Patton Model#s, but this is an older unit, correct? You may try contacting Patton (Owned by Holmes now so you may have to go through them)

If they cannot help you, try www.dtvintagefans.org There's collectors there that may have parts fans that they may be willing to sell a blade.

Alternatively, you may try Grainger, as they sell an assortment of blades. You will need to match a blade to your motor though, which should be fairly easy as the Patton fans use a common McMillan motor which most attic fans also use.

How did you pay for the heater? Cash, credit card, or check? What store did you buy it from?

If you paid by credit card, some stores can look the purchase up. Some stores will accept returns for an equal exchange based on lookup of the charge.
If by check, you can get a copy of the canceled check from your bank. Take the copy with the heater to the store that you bought it, and they will likely allow an exchange.

If you paid by cash, you can contact the manufacturer, and he will ask you for the date code or serial number of the unit (he will tell you where to look). You can then discuss with them how to proceed to have the unit repaired or replaced.