We all start from different fitness levels and some of us have more time to commit.
If you take 2 weeks off, it can take you 6 weeks to return to the same level of overall fitness. Be consistent and build slowly. Not knowing your background and a limited information about the type of riding that you have done over those 3 months; thus, we can only give general suggestions. To do a 200K ride, your currently weekly mileage needs to rise well beyond the current 75Km to perhaps 200Km per week but the most important ride is increasing the one long ride per week. You want to slowly build this long ride up as Macha indicated. You should not push hard on long rides. Your pace on long rides (currently your 50KM ride) should be moderate. Not slow but not fast.....in cycling Geekspeak....low Zone 2. You should be able to chat several sentences at a time. I would venture a guess that your anaerobic energy systems are getting plenty of workouts from the traffic lights.
I would not do more than one really hard Stava type ride per week initially but you do need one hard ride in addition to the long ride. Commuting should round it out for a while. You will get stronger. Just build slow and consistent.
On my commutes I will go hard when I get a series of green lights. It's short enough that I don't feel the need to pace myself too much. On my long rides I will go hard only during the second half for a few kms, then ride easy for a bit, and then do it again - cuz it's fun and I always seem to get a tailwind coming home! I average 19km/hr. Some weeks I will do both a long ride and a mountain ride. When I climb the mountain I go really slow, like really slow and then go nuts on the descent.
I just checked and I did 140k last week, and 65k the week before - because of the weather 2 long rides fell into the same week.