When spending duty at Character Creation the core book says you can choose each option once.

Does that mean I cannot take two XP bumps of+10, or does it mean I cannot take two XP boosts of the same type, like a +5 and+10 xp?

i have 15 duty to work with and wanted to turn it into the +5 and +10 xp. But I always thought that counted as the same option of XP

It just means you can't take the same exact option twice.

So for your example, with 15 Duty, you can't take the +1000 credits option twice to start with +2000 credits, nor can you take the +5XP option twice.

You can however choose to take both the +5XP and +10XP options, as they're different choices and start with +15XP if you so choose.