the whole legacy reset cycle is due to the limitations in the code, and part of the reason for the total rewrite. they want server cycles to last for months, years. legacy servers can't handle that.
Ironically, the decay system is the source of most of the performance problems. There are two decay systems, one for items deployed on the ground, and another for structures. Each system runs on every game server frame - 30fps - looping through all deployed items or structure components to see if the owner has used it within the decay time limit. The more structures and deployables you have, the harder the server has to work to find the abandoned ones.
If you disable the decay system and instead use a plugin to check for and dispose of unused structures, the server lasts for a couple of weeks before needing a reboot. You can set the following in server.cfg to cause the decay systems to do nothing each frame. Can't make it stop looping, but you can fool it into doing a noop. Since the server.cfg can't parse an exponent, use 9999999999 in place of the MaxValue. It's plenty long enough to make sure no decay event is ever triggered.
Code:
// Disable deployed item decay
// System.Single.MaxValue = 3.402823 x 10^38
decay.decaytickrate = float.MaxValue / 2
decay.deploy_maxhealth_sec = float.MaxValue
decay.maxperframe = -1
decay.maxtestperframe = -1
Code:
// Disable structure decay
structure.maxframeattempt = -1;
structure.framelimit = -1;
structure.minpercentdmg = float.MaxValue;