Difficult to be constructive in recommending anything unless you define a bit more what you want Tom, things to consider:
1. Another 15', or something shorter
2. You want to use the lines you already have, or are thinking about a change
3. New or used, budget
You can pick up some really decent kit second-hand, an original 15' Mackenzie DTX would be a great option, as would a David Norwich, (and many others
) but you could pick up a new Shakespeare Oracle 15' for around £100 and it will be significantly less through actioned than the Michael Marshall 15'
If you're interested in something cutting edge then the 15' rod that I have been most impressed by this year has been the LTS Complete Graphene , which I think is a deeply impressive 'second generation' Graphene rod - I'm not sure what the price point is for that, but it'll not be cheap.
H