Training advise/sessions to improve 5k time for sprint triathlon (18.52 time at the moment)
dunno... you seem plenty quick enough for me
are you doing anything structured at the moment (regular sprint/interval/tempo sessions, running with a club, track sessions... etc).
what sort of running are you doing in those 4 runs a week?
i guess you could try more high intensity sessions, depending on what the club track session is like. i'd be wary of doing too many though as you might increase your injury risk, and find it hard to get the recovery that you will need in. you could swap the tempo run for an interval or tempo set.
i'll be honest - if you have a coach at the club then they might be the people to speak to - if they are experienced then then will know what you are doing, how frequently, what sort of style/mental approach you have. i'm just a random on a forum that knows nearly bugger all about running but usually follow the approach that if you want to go faster then you need to go faster...
alternatively you could do some strength and conditioning work to build power. there are people out there who take this approach and have plenty of success.