I actually think three minutes is very good for most of the survival levels, from what I remember. Most normal levels are less than that, so it's not really a "scant" three minutes (in comparison to most levels).
I think possibly what may have caused your confusion is the relatively / seemingly low amount of money that those levels reward you with, which may make you think that the score is poor. But that is supposed to be that way: each campaign works its way up from low cache to higher cache, so don't be dismayed if (for example) you only start the first level of campaign 2 with a few hundred cache when you started the last level of campaign 1 with several tens of thousands of cache.
However, if you like, I can give you my own scores for each of those survival levels. I'll play through them today and tell you how well I managed to do on them.