Assuming you're above level 20, thus making the Lapras level 20, I would hang onto it for the time being. Lapras is difficult to come by. A pokemon's move set is more important than IVs, don't get me wrong; However, Dragon Pulse isn't all that bad. It isn't ideal, but it can still be very beneficial. You have to realize, if you place Lapras as a defender, people will use pokemon that are resistant to water and ice. Dragon Pulse give you some diversity.
The biggest factor is how badly you need Lapras. If you have had zero luck with getting a good Dewgong or Cloyster, dumping the candy into Lapras could be worth while. Also, it depends on what level you currently are and your other pokemon. With 28 candy (again assuming Lapras is level 20), you can power up Lapras to 24.5. If such a Lapras isn't going to be much use to you, there's no point in wasting the candy.
All in all, it's multifactorial. If you can answer "yes" to all of the following, I would do it:
(1) Is Lapras already level 20?
(2) Does Lapras have Frost Breath?
(3) Would you benefit from a level 24.5 Lapras?
(4) Do you have, or are you able to obtain, a decent Dewgong and/or Cloyster?
(5) Do you want have a dope defender and make everyone mad jelly?
Good luck, buddy!
