Hours are irrelevant and age "just" increases maintenance costs.
And yes, please do the D-Check on the aircraft you leased from "King Airways". It's a small company and support would be good!
No, seriously, paying for a D-Check takes about 2-6 month, depending on routes and cost. If you intent to fly an aircraft for a long time it's worth to do the check, if not, don't do the check.
But NEVER give back an aircraft that has less than 4 weeks left to a D-Check and 2 weeks to a C-Check. People will start to hate you if you do so due to automated checks.