The key is that your monthly wage slips shows at least the minimum threshold of £1550 each month for minimum 6 months.
Your employer needs to provide a written statement also.
Read the link to that thread I provided and follow the UKBA links in that posting. That's the best way to understand.
Personally, I would suggest you consider a small part time job just to get you clearly above the monthly minimum.
With 5 months wage slips at £2000 and one month at £1500 you'll get refused since UKBA will compute solely on the lowest in that 6 months
Good luck George