How much your electric bill will go up with the 1500 watt space heater will depend on your electric rates and how many hours you run the space heater per day.
If you run your space heater for 15 hours per day you would use 22,500 kwh per day. So if you pay 10 cents per KWH you would pay around $2.25 cents per day to run the space heater for 15 hours per day.
The space heater run for 15 hours per day for 30 days would cost $67.50
Space heaters are okay if it's just a little chilly out and you don't want to heat the whole house just yet. But if you're trying to save money on your natural gas heating bill then it's best to just turn up the furnace and heat the whole house instead.
Electric 1500 watt space heaters are very costly to run and it's cheaper to run natural gas or propane to heat your home.
If you try to heat your whole house with just space heaters then expect to have a heart attack when you get that bill of $500.00 or more and you're barely keeping warm.
I have an electric space heater but I only use it when my house is a bit chilly and then I only run the space heater for maybe 2 hours at the most per day.
Other than that I turn on my natural gas heating and only $150.00 per month to heat my home with natural gas where as I once tried turning off my furnace and using space heaters alone to heat my whole house and I got hit with a $500.00 electric bill for one month and my house was still chilly.
Space heaters are very costly to run and don't save you money.
Space heaters are okay for occasional use but nothing more.