Being fair:
Before reviewing death penalties in terms of server system, the ideal would be to review and reevaluate the deaths that occur icly.
First, that regardless of the punishment that the system imposes on the character, losing levels and xp, in addition to the time invested in recovering the lost xp, it would be necessary to establish clear rules icly to avoid abuses of pvp, in Icly terms of laws. Any fool can go off to kill other players-characters for any random reason. The problem is that many of the server rules or how they are applied do not cover everything. In terms oocly and icly.
So this leaves a lot to be pondered, since any player can take advantage of something that he considers appropriate or that has combined with the dm for some reason for a special moment, or the dm has passed this player the orientation, but the whole server does not know yet, giving a lot of room for mistakes, confusion or problems because have a lot of unknown stuff happening. Just my opinion.
Now, about the topic about death penalties...
Regarding the punishment for dying, in terms of system: a period of 72 ingame hours, with a reduction of saving throws, and having a reduced CON (1d4+1) would be plausible to represent the period of physical and mental recovery of the character, after being revived through a cleric npc. Finding a cleric pc can work in a different way, instead 72 ingame hours, only 24 hours. Because this incentive the clerics players to roleplay as true clerics and follow they own behavior of clerics. The "resurrection sickness" can't be removed by removing curse, only a dm can remove it if necessary, for matter of event or to fix a bug.
Reduction of xp? Losing less xp after lvl 15 would be interesting, but that would be too comfortable. Keeping the current punishment would be acceptable, 5 to 15% loss is reasonable, as long as dms have good sense when launching spam against players in dm events, and are aware that not always invincible mobs or too many mobs is the same as challenge. I already consider it exaggerated when they send more than 3 to 5 mobs to each character in the event because the intense lag or too op to deal... And there are events that I watched in the past about having more than 12 mobs for each player.
Cost of gold? Keep. high enough for causal and even hardcore players.
The current problem about the penalties for higher-level characters is about punishment after being revived.