I find a lot of subjectivity in the ratings given, so I'll be as objective as possible.
The idea is interesting; the writing can be improved a lot since it has some errors (not to say many); That the mc is Japanese seems a bit out of context, but it doesn't interfere much with the future development of the story; the mc's personality is passive and if although he suddenly seems to be shouting orders, in reality he is very passive being that he can perfectly silence the ideas of his subordinates by sending a ki attack to those guys, after all, they are quite weak; the progression of his powers is slow, too slow if we think that he spent 15 years trying to adapt to his body and training, we have to think that freezer trained almost 1 year to reach gold freezer, I don't think it took 15 years to adjust his strength, it is illogical considering the monstrous capabilities of Frieza's body; the way it handles time and the timeline in the chapters is not the best, an example of this is spending 15 years in a single chapter...
So far those were the things I found, I hope the author's writing will increase its quality.