Some toilets are just duds. Can't say if that's the case on yours. But, if things are slow to flush, there are a few things you can check.
The siphon jet on that type of toilet may have some mineral deposits in it. Or, there may be some foreign object caught in it. That's what starts the flush. But, if there's something caught in the trapway, or in the line, that can slow down or prevent it from flushing properly.
One quick test is to fill a large bucket, and pour it quickly into the toilet to see how it handles it. It should flush itself if you pour it fast. If you then try to pour it slowly, you should get the whole bucket emptied without the level rising much. When you stop, it should return to the original height in the bowl. If the bowl now is at a higher level, you may have found your problem.
The tank AND bowl must be full for it to flush properly. IF the bowl starts out lower than it should (the fill valve stops when the TANK is full, it assumes the balance of flow between that and the bowl is proper to get the bowl full), it won't flush properly. A common problem is if the hose in the tank is not filling the bowl...it must be positioned properly. Or, if you've changed the fill valve and it's not an OEM version, the balance between the bowl and tank is not correct. There are adjustable aftermarket ones, you don't have to use an OEM one.