It varies a little depending on the bank, but the most common approach is to take the average bonus of the last two years, then add 50% of that figure to your basic salary, i.e. add around €7.5k in your case. If you really wanted or needed to take more of it into account for the 3.5 times assessable income limit, then PTSB would probably be your best option.
Best regards,
Dave Curry CFP®
https://www.linkedin.com/in/davecurryirl