It wasn't rubbish when it was new. It's second hand and if it says before the serial number MP70NT
(N = made in UK, T = traditional style case) then it was made in the UK Yamaha-Kemble factory, distributed in the mid 90's to early 2000s. Based on the E110(T), although it has non underfelted hammers it does have a decent spruce soundboard, good build quality and action. It may seem cheap today at £1,500, but new in 1995 these were selling discounted for only £2,500 - Yamaha's piano prices have increased way ahead of most goods, as they were very underpriced in the good old days, whenever they were.
The smallest of Yamaha's uprights and similar to the current B1/2 a well tried and tested piano, reliable, the downside is that it's short, so ensure you're happy with the bass quality and the feel (very short pianos are proportionately less deep, consequently most have short keys which means they're less easy to play, especially when one or some of your fingers have to be close to the fulcrum.)
Ask the dealer for the age even though condition is just as important in assessing its value. If it's in good order and comes with at least a year's guarantee (especially because of the electronics) then £1,500 seems a very good price from a dealer.