Worth telling us what you did, where you did it and what social security you paid in the 15 years abroad.
If it was UK which you imply above then you should investigate the options you have to pay additional UK national insurance contributions - it can make a huge difference and is incredibly cheap. You can pay class 2 National insurance contributions from abroad which is a couple of hundred pounds a year and potentially get your UK pension to a full UK pension (you can usually only go back 6 years but there's an exception on the time limit until 2023 for some years so likely you could pay last 12 years and then keep paying). It is possibly the single best investment you could ever make.
You can get some info if you google "paying UK NI contributions from abroad" (won't let me link) but when you apply for you NI history it will tell you which years you can make up if you choose. They are helpful on the phone too when you eventually get through.
Really you have to do the maths on what's best:
- Partial pension from each that just happens from what you are working and paying now
- Full irish pension (by using your UK NI contributions towards your irish pension)
- Pay additional UK contributions and take partial irish pension plus greater (possibly full) UK pension
If you are eligible, option 3 is usually always the best (and not a large gamble now as you are only investing £200 a year and as long as you live to 69 it will be the best investment you can make) but do the maths and check out all the facts first. I also like this because it hedges your bets against rules changes in the future, means testing in either UK or Ireland or both, currency changes etc. This is important to note - pensions have changed a lot in last 20 years and will have to change considerably more in the next 20 years - all you can do really is keep your options maximised. This is my personal take from when I investigated for my wife who was in similar circumstances (and regretted that summer job at school that wrecked her average method!!!!) - do not take it as financial advice - just advice on where to investigate what's possible.