Err, no.
It may be using 15 - 20% of its total military power - (in fact, it's probably more) - but that's pretty much its entire deployable force. Remember that this is a peacetime army with a large % of non combatants. So that 70 - 80%? of non-deployed troops are clerks in Moscow, missile techs in Archangelsk, border troops deployed in Vladivostok on the PRC border, naval sonar operators in Leningrad and staff college dudes in Smolensk. Those people aren't going to carry AK's in Donbas.
It's well documented that RUssia is force conscripting grandads in Luhansk and using them as cannon fodder with World War 2 bolt action rifles. Russia is offering large bounties for kontraktnik soldiers to sign up in Moscow. The war is clearly not going well and there's shit all available to perform any offensive that's larger in scope than seizing a little village here and there every couple of weeks.
And it's clear that Ukraine doesn't have the manpower or the inclination for frontal attacks through urban areas. That sort of op eats up Stalingrad scale numbers of infantry. Instead, the Ukrainians are blowing up arteries and ammo dumps to try and force the Russians to pull back due to lack of ammunition and other supplies.
So few corrections here, they are uaing 10% of their active deployable force, conscripts dont count, ans they are currently not engaged in fighting.
This said, all is fair in live and war ans they all lie when reporting to embelish success and cover up faliures,ike Russia did at the beggining of the campaign.
Now, since they are taking large swats of land, now you need forces stationed in occupied areas to secure them, so now you dont need well trained troops, those go to thw front, but you keep new regruits in the rear, training and serving as rear guard, as well as gaining experience and getting more battle ready.
You will see more of this as the campaign goes on, and more major cities are taken.
In Russia it is bussiness as usual, planes fly, ppl go to work, and kids to school.
While Ukraine is unable to hold off the 10% advance.
Also worth mentioning is that foreign armies are elsending thsir officers in to gain combat experience and hands on training.