Is the yield not calculated with my outstanding balance I.e. 15,600÷150,000= 10.4 %
The ‘gross yield’ is total cashflow (the rental income in your case) divided by the value of the asset (the apartment valuation you supplied). So, (15,600/290,000) = 5.4% per annum. This is a comparable measure of how much rent you can get out of a unit right now at today’s rents and property valuations. This differs across housing types and areas of the country. You might find it is higher for 1-beds or 2-beds in Dublin city compared with larger Dublin city properties and you will likely find it is higher in the countryside than in Dublin.
The gross yield does not take into account expected changes in the rent or property price. So, you might think you have an unusual property that should see high prices rise or rent rises over time and that might allay concerns about a low current gross yield. For instance, you might think the property is in a well-located, but rundown area that might improve over time. But that’s a gamble and you could instead move your money elsewhere instead.
The gross yield also doesn’t take into account the costs of maintaining the property or paying tax. You ultimately care about the amount of money ending up in your hands at the end of every month. Your costs seem high and are pushing down your “net yield” quite a lot.
The typical gross yield cited by investors is for a situation in which the investor owns the property outright with no mortgage. In your case, you have debt and so your net investment position at present in this BTL is actually only (290,000-150,000) = €140,000. You own the property, but the bank needs to be paid if you ever sell. You didn’t put €290,000 cash into the investment, you only put up your deposit initially and have keep whatever price increases you’ve enjoyed since then locked up in the property. In the jargon, you are using “leverage” to lever up your gross yield to (15,600/140,000) = 11.1%. Notice, however, that you can arbitrarily raise your gross yield by taking on more and more debt! Say you refinance up to 70% LTV, then you could push your gross yield up to (15,600/(290,000-(290,000*0.7))) = 17.9%. You could then use the extra ((290,000*0.7)-150,000)= €53,000 for some other purpose. This is very tempting, but it was also a large part of the downfall of Celtic Tiger investors who thought the sun would always shine. Yields are the return side of the investment, but you can’t forget about the risk of vacancy, rental decreases, and price declines. The more debt you have, the greater the difficulty you will have if things go sour. Your net investment will get wiped out by modest price declines, but the bank will still need to be paid. Imagine you had also used the €53,000 to buy another BTL and so on and so on. Some people fool themselves into thinking they are a genius investors because they are taking wild risks.
The gross yield and net yield on your apartment seem quite low. I would be willing to bet that you’d find better investment properties out there than this one if you were determined to remain a landlord. And I would again stress that BTLs aren't your only option. You could quickly clear both mortgages and invest through your current income into tax-relieved pensions. But that's a matter of preference and risk appetite.
There’s a lot of material online that might help clarify things for you and it would be really worth your time.
https://www.auctioneera.ie/rental-yield-calculator