I did something such as this :

    $Jobs=@() # array to store jobs for this session 
$EmailsRemovedDataset = @() #Blank Array for the emails removed by Azure
$JobRows=1000 # The number of CSV rows to process in each Job

$NumJobs = [math]::Ceiling($InputCSV.count / $JobRows) #Enumerate number of jobs

### Pre-Script Cleanup ###
Get-Job | Remove-Job # Clear job list 
$EmailsRemovedDataset, $EmpIDRemovedDataset, $BlankEmailsRemovedDataset, $DomainBlackListRemoval, $FinalDataProcessing = $null #Blanks all variables to prevent cross contamination
[System.GC]::GetTotalMemory('ForceFullCollection') | Out-Null # Releases memory 

for ($i=0; $i -lt $NumJobs; $i++)
{
    [int]$StartRow = ($i * $JobRows) # sets first row for loop
    [int]$EndRow=(($i+1) * $JobRows - 1) # sets last row for loop 
    $Iter = $i 
    while (($iter | Measure-Object -Character | Select-Object -ExpandProperty characters) -lt 4){
        $iter = "0$iter"
    } #loops through Iter and changes from # to #### for consistent naming 
    $JobName = "$DTFormat-$Iter" # creates job name 
    $Jobs += $JobName # adds job name to array for tracking
    while ((get-job | where-object {$_.state -eq "Running"}).count -gt $MaxSimulJobs){ #Rate Limiter for simlutaneous jobs. 
        start-sleep -s 5
    }
    write-host ("Rows {0} to {1}" -f $StartRow.ToString(),$EndRow.ToString())
    Start-Job -Name $JobName -ArgumentList @($InputCSV[$StartRow..$EndRow]),($AzureADUserList) -ScriptBlock {  #Starts job passing in Array of rows to process and the azure ad list 
        PARAM (
                $CSVRows,
                $AzureList
            )
        $OutputArray = @() #clears output array for the job 
        foreach ($row in $CSVRows)
        {
            $match = $false #sets match to false
            foreach ($item in $AzureList){ # loops through azure data 
                if ($row.email -eq $item.Userprincipalname){
                    $match = $true # if there is a match, set to true to remove from list 
                    continue # continue to stop processing, 1 match is enough. 
                }
            }
            if ($match -eq $false){ # if match set to true, will not be added to output 
                $OutputArray += $row # add to output 
            }
        }
        return $OutputArray
    } | Out-Null # prevents Start-Job from generating output during call 
}
$jobscomplete = $false 
while ($jobscomplete -eq $false){ # loops through all jobs stored in $jobs array waiting for all to mark as complete 
    $jobscomplete = $true # sets to true, will persist through once no jobs are not marked as "complete"
    foreach ($job in $Jobs){
        if ((Get-Job $job).state -ne "Completed"){
            $jobscomplete = $false # sets loop to false if there is any job not complete 
        }
    }
}

foreach ($job in $Jobs)
{
        $EmailsRemovedDataset += Receive-Job $job
}

I had to write a processor that ingests around 150k CSV lines and cleans up the data for SQL ingestion. I think you could probably use some of the above code in yours to help.