Newb seeks help on Oilrig

I'm new to Xonotic, playing with an older PC on Ubuntu.
I'm running through single player on Hard until i get the hang of it. My PC hasn't had any issues until I got to the deathmatch on Oilrig.    My PC completely glitches out.   Bots appear and disappear, I shoot dead on and miss, I get killed by adversaries I never see.  I can't get past this level.
Like I said, I havent had this issues on any other level.
Any suggestions besides "Get a new (PC, Graphics card, CPU)"?

Pallama

Are you having fps issues on this map perhaps?

Also might as well join regular servers, people are very helpful there!

What level of detail, effects and resolution are you normally running the game at?

Thanks all.  
I have dumbed down the FPS and resolution to very low levels and the game is still way to glitchy.  
I’d like to practice a little more on single player and one man games to learn maps until I get better.  Is there some way to edit the singleplayer logs so that I can play levels beyond oil rig without going though Live Die Repeat Edge of Tomorrow 5000 Times?
Mario I’ll probably show up soon as Pallama or A_VERY_OLD_MAN

Thanks in advance.

Dumbed down the FPS (frames per second)? If the number is very low, the game will feel "glitchy".

You can skip levels by using g_campaignxonoticbeta_index in the console (open: Shift+ESC). Since Oil Rig is level 19 you can enable the next one with: g_campaignxonoticbeta_index 20

Honestly, you don't really need the singleplayer campaign even. There's no lore, no reward after completing it or anything worth grinding for, they're essentially just custom game presets which you could make yourself just as easily.

Thanks all. I enjoy campaign mode.  I don't get enough time to play, and I'd be useless in MP mode until I get some skills down like bunny turns, laser jumping, etc.

g_campaignxonoticbeta_index 20 worked great, thanks Mirio

Honestly, you don't really need the singleplayer campaign even. There's no lore, no reward after completing it or anything worth grinding for, they're essentially just custom game presets which you could make yourself just as easily.

I hope there is still people to enjoy a game by itself without reward other than the game itself and without the idea of grinding at all.

Btw I agree on the lore part, but it looks like that's if there is place for lore it's not a problem to not have.

I mean it's better to make place for lore than to reward and worst, grinding. There is no reward neither grinding in a book or a move, but a lot of lore. Same can be for games. And if there is place after lore, why not rewards. I'm still looking for a real reason for grinding. 

Even before lore, making the campaign player enjoyable is the first thing to do: exciting scenarios, interesting challenges etc. First reward must be the joy to play.

For some curious reason I'm still playing the campaign of Quake 3 Arena, even if the lore is a 42 seconds CGI sequence without any words but grunts.