save a variable or multiple variables within a php variable

I send this data by POST hasta #producto_15 if I do #producto_16 no longer saved in my bd by the structure it has.

<div id="producto_1" class="row form-group productoss">
<input type='text' name='nombreprod1' placeholder='Nombre del producto'>
<input type='text' name='skuprod1' placeholder='Sku' required>
<input type='number' name='cantprod1' placeholder='Cantidad' >
<input type='number' name='cosprod1' placeholder='Costo' >
</div>
<div id="producto_2" class="row form-group productoss">
<input type='text' name='nombreprod2' placeholder='Nombre del producto' >
<input type='text' name='skuprod2' placeholder='Sku' required>
<input type='number' name='cantprod2' placeholder='Cantidad' >
<input type='number' name='cosprod2' name='cosprod' placeholder='Costo' >
</div>
...

And the processes in a PHP

$pro1 = $_POST['nombreprod'];
$pro2 = $_POST['nombreprod2'];
$pro3 = $_POST['nombreprod3'];
$pro4 = $_POST['nombreprod4'];
$pro5 = $_POST['nombreprod5'];
$pro6 = $_POST['nombreprod6'];
...

I want to check if each one exists and if there are stored in a variable, delimit it and keep it in a database. Something like this:

$nomproductos = $pro1.$pro2....$pro50

They recommended me to put everything in a variable to save it in a column called "product" since for now I am saving in several columns (and I can only add 15 products) I was doing it so far:

INSERT INTO productos (sku01, sku02, sku03, sku04, sku05, sku06,
    sku07, sku08, sku09, sku10, sku11, sku12, sku13, sku14, sku15, pro01, pro02, pro03, pro04, pro05, pro06, pro07,
    pro08, pro09, pro10, pro11, pro12, pro13, pro14, pro15, cap01, cap02, cap03, cap04, cap05, cap06, cap07, cap08,
    cap09, cap10, cap11, cap12, cap13, cap14, cap15, cxp01, cxp02, cxp03, cxp04, cxp05, cxp06, cxp07, cxp08, cxp09,
    cxp10, cxp11, cxp12, cxp13, cxp14, cxp15, cop01, cop02, cop03, cop04, cop05, cop06, cop07, cop08, cop09, cop10,
    cop11, cop12, cop13, cop14, cop15, subto) VALUES
    ('$sk1', '$sku2', '$sku3', '$sku4', '$sku5', '$sku6', '$sku7', '$sku8', '$sku9', '$sku10',
        '$sku11', '$sku12', '$sku13', '$sku14', '$sku15', '$pro1', '$pro2', '$pro3', '$pro4', '$pro5', '$pro6',
        '$pro7', '$pro8', '$pro9', '$pro10', '$pro11', '$pro12', '$pro13', '$pro14', '$pro15', '$cap1', '$cap2',
        '$cap3', '$cap4', '$cap5', '$cap6', '$cap7', '$cap8', '$cap09', '$cap10', '$cap11', '$cap12', '$cap13',
        '$cap14', '$cap15', '$cxp1', '$cxp2', '$cxp3', '$cxp4', '$cxp5', '$cxp6', '$cxp7', '$cxp8', '$cxp9',
        '$cxp10', '$cxp11', '$cxp12', '$cxp13', '$cxp14', '$cxp15', '$cop1', '$cop2', '$cop3', '$cop4', '$cop5',
        '$cop6', '$cop7', '$cop8', '$cop9', '$cop10', '$cop11', '$cop12', '$cop13', '$cop14', '$cop15')

As you can see it was a good option to list 15 products. If I had not killed hours in san google would not come to bother life, I spent 2 months learning php, thank you for your answer.