It would depend on your level of experience and goals with playing. If you are just getting started and want something decent to play, and plan to practice often, you will likely have a strong urge to replace either model with something more substantial in the near future. In that case, I'd get the 223. I'd probably get the 223 regardless, but I'd have to think about it more.
The 223 is only three years older than the 155. The main difference is that the 155 has the "CF engine", with key off samples, sustain samples, more polyphony and such. To be honest, these things do not matter much, although I admit the key off samples make a large difference in sound for me. The sound on the 223 will be rather bright compared to the 155, which may be a positive or negative for you. The 155 sounds virtually identical to the modern Clavinovas.
I'd go for the 223 with the assumption that you will have something to replace it within a year anyway. I only lasted four months on my Yamaha S31 before I wanted better sound, keys, and pedals. Save your money and get the 223 unless you are an ultra casual player and do not foresee wanting a new piano under any circumstances. Even then, you may still be tempted to upgrade.
PS: my S31, which is newer but significantly worse overall than the 223, sells for $600-700 used on Kijiji here in Ontario. $650 for the 223 is a steal in comparison.