As there has not yet been any S.20 consultation (from what you say) the estimate you have is not a bill - I guess the intention is to give advance warning. Hopefully the estimate explains what works are envisaged - the Service Charges need to be reasonably incurred (ie genuine repairs/maintenance or for services actually delivered) and the costs for such items need to be reasonable in extent (so painters can't be charged out at £500 per hour). Depending on what works are covered by the estimate, the £6,000 (if that is what it comes to over 4 quarters) could be for reasonable items of work and at a reasonable cost for those works. Watch out though for works that straddle more than 1 service charge year - the figures you have are likely to be just for the service charge year concerned, but this does not necessarily mean that all of the project costs fall in that year.
I know that a lot of work that has backed up is now moving forward in earnest, so I suspect most blocks will see big increases in the service charges for what amount to major works projects. The figures for Great Arthur House are enormous - but that is very much the exception due to the scale and complexity of the work.