- Developer time is expensive.
- 80% of the code consumes 20% of resources and vice versa.
From this it follows directly that it is necessary to engage in optimization when it is impossible to do without it. If you are not limited by anything and do not force you to write on C / C ++ for Android (usually these are old libraries that have been written for a long time and will be more expensive to rewrite them in Java), then you should write in Java. In terms of performance, it is important to rewrite in C / C ++ only the part that is actually a resource.
PS For Qt for Android there is a port: Necessitas . But this is an additional artificial layer, and its use will almost always be to the detriment of the result.