Standard spark plugs

[kiwipom]

I have a 1997 XK8 & recently purchased it.
It was serviced 2000kms ago (1400 miles ?) & I have discovered that the garage put standard plugs in it NGK BKR5E-11...V-power.
I was not too pleased so when I took it up with them, they showed me a reference sheet stating that standard plugs are an alternative to platinum/iridium.
The mechanic said there should be no issues as long as I change them every 15000kms (10000miles)...the XK drives okay...so does anyone know what the downside is with these standard plugs ???
I took one plug out & it is new & clean and the correct colour...
Feedback please.
thanks

[NormanD]

Sorry can't give you the correct number but the correct one have something like a 30,000 + range

[mike020150]

Jaguar fitted different plugs to different emission versions of the V8. The 96 to 09/97 engines (97 MY) used the BKR6EVXA-11. The next version (98MY) used the BKR5EVXA-13 plug. Later cars switched to the long life iridium plugs albeit at a horrendous replacement cost plus a tendency to corrode in when left untouched. Mike.

[kiwipom]

Sounds like I should be using BKR6EVXA-11's or equivalent.
Just found information in Jaguar owners handbook (Car care, specifications 6-1) saying BKR5E-11 (standard plug) is recommended where leaded fuel is used.
I thought leaded fuel went out long before the XK8 appeared.
These standard plugs were fitted before I owned the XK8, but I'll bet there are a few more XK8's running on standard plugs without the owners knowing it (non-specialist garage servicing)
I'll change my plugs, but I have no 'comeback' on the garage as (in theory) the've done nothing wrong.
Thanks for the feedback