It should be 0%. Catch up to what - for what? So we can go do some drone bombing in Africa like a proper western nation? Is that the plan? I guess it's easier to give the guys with the big guns what the want, instead of actually staying true to the values of demilitarizatizing the planet.
It should be 0%? If men were angels, I guess. How do you propose that we demilitarize the planet, without a big stick to whack down the bad players that will inevitably arise?
if you tell russians to take down their weapons, their will be no war. if you tell ukrains to take down their weapons, they will loose their country.
it's not as easy as you wish, besides that I would prefer like you would describe, unfortunatly as long as there are borders/humans/whatever there will always be conflicts.
The NATO alliance - and EU - is going to need a lot of hardware and technology to stop Russia if it's going to arm-up and empire-up, if it plans to take Ukraine with the help of Belarus and then potentially move on to other targets after that (Baltics, Moldova, Poland, Sweden, Finland, whichever). Russia has clearly taken over Belarus here, this is the USSR beginning to march with multiple armies again. If Putin redirects his nation into a persistent war footing, and redirects his nation's resources into war mode (shifting to mass killing the opposition outright as in the old days, Stalinification), then for a stretch of time that will be a very dangerous, very potent effect and will enable Russia to push outward militarily in a way they otherwise wouldn't be able to (and yes it'll run out of fuel eventually, as it's a rapid depletion move, but for N years it'll be a very potent adversary).
$150 billion might not be enough, unless Germany plans to play no role in defending the eastern flank of NATO as Russia marches. They have been badly underfunded for decades, $150b is a down payment on catching up.
Putin's Russia is going to be in an economic and political swamp for a long time for this, it wouldn't be surprising if he chooses to move on to a new target promptly after Ukraine just because why not. The same crazy calculation that gets us here, it isn't too far of a stretch from there to argue (if you're Putin) for trying to take some of Finland's territory.
Germany needs to take this very seriously and I think they're beginning to.