Sybase SQL - Truncation error occurred. Command has been aborted

Need help with below code, as it fails with truncation error

Truncation error occurred. Command has been aborted.

create table monCacheQuality (
        ServerName sysname
        ,CollectionDateTime smalldatetime not null
        ,PhysicalWrites decimal(15, 0) not null
        ,PhysicalReads decimal(15, 0) not null
        ,LogicalReads decimal(15, 0) not null
        ,CacheQuality decimal(15, 0) not null
        ,CacheHitPct decimal(15,4) not null
        )

-- Main code starts here 
declare @physical_read1 decimal(15, 0)
    ,@logical_read1 decimal(15, 0)
    ,@physical_write1 decimal(15, 0)
    ,@cache_search1 decimal (15,4)

declare @physical_read2 decimal(15, 0)
    ,@logical_read2 decimal(15, 0)
    ,@physical_write2 decimal(15, 0)
    ,@cache_search2 decimal (15,4)

while (1=1)
begin
    select @physical_write1 = PhysicalWrites
        ,@physical_read1 = PhysicalReads
        ,@logical_read1 = LogicalReads
        ,@cache_search1 = CacheSearches
    from master..monDataCache

    waitfor delay '00:00:20' -- Log every 20 sec

    select @physical_write2 = PhysicalWrites
        ,@physical_read2 = PhysicalReads
        ,@logical_read2 = LogicalReads
        ,@cache_search2 = CacheSearches
    from master..monDataCache

    insert monCacheQuality
    select @@servername as ServerName
        ,getUTCdate()
        ,@physical_write2 - @physical_write1
        ,@physical_read2 - @physical_read1
        ,@logical_read2 - @logical_read1
        ,case 
            when @physical_read2 - @physical_read1 = 0
                then - 1
            else (@logical_read2 - @logical_read1) / (@physical_read2 - @physical_read1)
            end as CacheQuality
        ,100-(((@physical_read2-@physical_read1)/(@cache_search2-@cache_search1))*100) as CacheHitPct
end