"Is a short leasehold like this reason enough to walk away? "
Maybe; maybe not. I am afraid that without reading the title and seeing what (if any) reason there is for such a short lease term, it is impossible to advise. Certainly, the short lease term is enough to raise a red flag, at least in Ireland.
If your solicitor is unsure as to the legal consequences of the lease term in this case, you could ask him\her to get a written opinion from conveyancing counsel (which should not cost more than €400 plus V.A.T. unless the title is extremely lengthy\complex)