Bro, The test pilot for Liaoning once mention Russia angle deck of Varyag are too conservative. It can be further raise by another 10 degrees for maximizing loading take off. J-15 are incoporating some of the latest manufacturing technique which results in further reduction of weight, like using composite.
J-11B are reported having 700kg weight reduced compare to Russian Su-27SK. Su-33 manufactured using old techique and full metal aircraft based on Su-27SK. Chinese J-15 will definitely weight lighter than Su-33. And the final blow is domestic Taihang engine for J-15 will have higher thrust than AL-31F engines, comfirmed by spokesman for Ministry of Defence China.
All this will give it a far superior thrust to weight ratio than russian Su-33. russian Su-33 are reported capable of taking off full fuel loaded but can carry only 2 WVRAAM and 2 BVRAAM. Imagine with the angle deck raise, higher thrust engine, lighter weight of the airframe. It is possible without catapult, J-15 is able to take off with full weapon loaded. The downside will be the J-15 needs to use afterburner to achieve max thrust for that take off but J-15 is a big bird capable of carry plenty of fuel.
The American continue use of catapult is because their F-18E/F has a smaller airframe compare to J-15. Fuel to them is precious. Catapult allows the F-18 with full load to take off without using afterburner. Therefore increasing combat radius.
Let me show you another thing.
See from 4.30mins onwards.
From that video, A C-130 hercules is able to take off from a flat deck, Yes, it needs to start from back of the deck to do the take off. But imagine the front is angle deck, The heavy plane needs not to take off all the way from the back but the third launching pad position. With angle deck, it will able to lift off the propeller plane. Same as for our Y-7 AEW which will enter service in future and definitely able to serve in CV-16 Liaoning. Modern angle deck will serve all our carrier wings in future without the need of complicated catapult that eat up precious spaces and resources of the carrier.